The present invention relates to a device for fixing the fractured ends of a bone in a living body by means of a nail or a plate which is connected with the bone.
Marrow nailing and the external application of long plates are generally known and medically tested procedures for fixing fractures in long bones. The nails, generally, either have a continuous slot and a cloverleaf-type cross section, or have a circular cross section and a slot which ends in the upper region of the nail.
The significant drawback of a nail having a continuous slot is that, on the one hand, for biomechanical reasons and due to the provision of the slot and the requirements for elasticity, the nail has a cloverleaf configuration but, on the other hand, comes into contact with the bone wall only in very limited longitudinal regions, i.e. is lacking as regards transverse clamping in the femur.
A comparatively high rate of cracks and tearing has been found with nails having a noncontinuous slot and a partially circular cross section.
The cracks always start at the end of the slot, and in the plate they start between two bores for the connecting elements. In the interlocking nail, they start at the holes for the transverse bolts. As a result of experimental tests and study, it has been found that a finite slot, in particular, in which the flow of forces is deflected around the end of the slot, enhances crack formation.
Providing the slot end with an additional notch, as had been done in the past to prevent crack formation, makes this effect even worse.